Compilation warnings in regex.c on macOS Mojave with the Homebrew distribution of gcc version 4.9.4_2

[Thomas Shields]

My configuration is somewhat weird, and this is a very small point given that gcc 4.9 is essentially obsolete and this is only a set of warnings, but it may have other impacts, so I’m reporting it.

1. gcc 4 doesn’t support the preprocessor operator “__has_attribute”

2. Compiling “regex.c” from Gnulib with the macOS Mojave Homebrew distribution gcc 4.9.4_2, my “config.h” (attached) gets included twice, since the Gnulib “libc-config.h” doesn’t have a preprocessor guard. (NOTE: adding a guard should be the easy fix)

3, The 1st time is via “libc-config.h" in “regex.c”, the 2nd time is via "libc-config.h” via “dynarray.h” via “regex_internal.h”

4. After the 1st pass through “config.h” with “__has_attribute" undefined, gcc-4.9 eventually includes “cdefs.h” from the macOS Mojave "Command Line Tools for Xcode 10”, which defines “__has_attribute” as below:

#ifndef __has_attribute

#define __has_attribute(x) 0

#endif

5. The 2nd pass through “config.h” with “__has_attribute” thus defined then results in a different definition of the “_GL_HAS_ATTRIBUTE” (and related) macros

In file included from ./libc-config.h:33:0,

                 from ./dynarray.h:22,

                 from regex_internal.h:36,

                 from regex.c:70:

../config.h:668:0: warning: "_GL_HAS_ATTRIBUTE" redefined

 # define _GL_HAS_ATTRIBUTE(attr) __has_attribute (__##attr##__)

 ^

In file included from ./libc-config.h:33:0,

                 from regex.c:23:

../config.h:670:0: note: this is the location of the previous definition

 # define _GL_HAS_ATTRIBUTE(attr) _GL_ATTR_##attr

 ^

I’m using a version of Gnulib downloaded from the repository on 2/9/2021 @ 12:54PM CST.

My workaround is to add “-D__has_attribute(x)=0” to “AM_CFLAGS” in my Gnulib “Makefile.am”.

If you need additional context, just ask.

Regards,

Tom Shields

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